96 The American Geologist. Feb. i8«i 
what are the maximum .soundings in the river, yet the <>1<1 channels 
are so filled with Drift that their depths are not revealed. Still, 
we know that in one portion of the channel cut out of limestone 
and more or less tilled with Drift, the sounding is 120 feet. A 
short distance beyond, the channel across the Laurentian gneisses 
shows soundings of 240 f»et. The maximum depth of the lake- 
basin is 738 feet. The deformation recorded in the beaches is 
more recent than the episode of the upper till. Consequently, 
if the continent were at a high level, with the warping, known to 
have occurred since the Drift was deposited, removed, as shown 
by the above figures, there would be not only no barrier, but a 
sufficient slope in the Laurentian valley for the drainage of what 
is now the ( Ontario basin. 
Furthermore, the presence of the rock barriers of the rapids of 
the St. Lawrence, further east, are wholly accounted for by the 
terrestrial warpings of the region. Hence, I have demonstrated, 
after a decade of study, that no barrier existed across the Ontario 
valley when it was being carved out by the ancient St. Lawrence, 
and that this barrier is of quite modern origin. 
South-east of Georgian bay the average measured warping is 
tour feet per mile, in mean direction of X. 20° E. This will ac- 
count for a portion of the barrier closing the Georgian outlet of 
lake Huron. The more elevated beaches in the region of lake 
Huron record a still greater change of level. 
At the outlet of lake Erie, Mr. Gilbert and myself find a differ- 
ential uplift of about two feet per mile, and this is sufficient to 
account for the recently formed basin of lake Eric. 
The warping affecting the Michigan basin has been that towards 
the north and east : and even in the buried channels south of 
lake Michigan there is no evidence of an ancient drainage to the 
south, as their beds were too high compared with those of the 
northern, although the latter have been elevated recently by 
warping. 
1(1. Conclusions from the observations. 
The valleys of the great lakes here studied are the result of the 
erosion of the land-surfaces by the ancient St. Lawrence ( named 
Laurentian) river and its tributaries, during the long period of 
continental elevation, until the streams had reached their base- 
lines of erosion, and the meteoric agents had broadened the val- 
